Field of the Invention
The invention relates to the protection of turbines of hydro-electric power plants installed on civil waterworks, from the debris carried by the water, as such debris is likely to deteriorate or affect performance if it passes through the blades wheels of the turbines. The invention relates more specifically to the removal of the floating debris stopped by the grating of grating assemblies equipping such hydro-electric power plants, without such debris passing through the impellers of the turbine units.
The invention relates to the case of a hydro-electric power plant of known type, comprising a turbine unit, including:                a supporting structure in or parallel to the main plane of the assembly, comprising a closed main portion in which is located a cylindrical housing with upstream and downstream openings, and an upper portion with an opening,        and a turbine with impeller, in particular with blades which may be more or less tilted, mounted in the housing, which may have an immersed downward position where the unit is tilted from upstream to downstream and from the bottom toward the top.        
A first object of the invention concerns a hydro-electric power plant for civil waterworks that includes a channel for flowing water limited by a structure having a bottom slab and two walls forming side walls, said plant comprising, operatively associated, a downstream turbine unit as just defined, and an upstream grating assembly which allows the inflow of water.
A second object of the invention relates to a grating assembly intended to be operatively associated with a turbine unit in order to form such a hydro-electric power plant.
A third object of the invention relates to a method for implementing such a hydro-electric power plant, for the purposes of discharging the floating debris stopped by the grating.
Description of the Related Art
Document FR-A-2862723 discloses a turbine unit for a hydro-electric power plant of the type which is the object of the invention. Such a hydro-electric power plant is intended for equipping a watercourse where there is a very low drop of less than 10 meters, and preferably from 1 to 5 meters. It comprises an impeller, the ratio between the kinetic energy of the flow of water exiting the impeller and the potential energy of the drop being less than 20%. The turbine unit is equipped, on the upstream side and opposite the opening of the impeller housing, with a water intake grating that is adapted and intended to stop, on its upstream side, any debris carried by the water of a size that is greater than the size of the openings through the grating. In addition, the turbine unit is equipped, on the upstream side where the grating in question is located, with a scraper with rotating arms associated with the grating and having the function of scraping off the debris that accumulates on the upstream side of the grating.
In embodiments of this type, there is often also a water intake pre-grating adapted and intended for mounting in an upright position in and across the channel of the civil waterworks, upstream of the turbine unit. This pre-grating has openings that are larger than the openings through the grating equipping the turbine unit. Thus, the pre-grating is adapted and intended to stop the larger debris carried by the stream of water, while the grating equipping the turbine unit is adapted and intended to stop the smaller debris. The pre-grating and grating therefore combine their effects. Such a pre-grating is part of a grating assembly allowing the inflow of water which, in addition to the pre-grating, further includes means for associating the pre-grating with the supporting structure of the turbine unit, or more frequently with the structure of the civil waterworks.
Document FR-A-2531118 describes such a pre-grating which is fixed and tilted, which casts doubt on its effectiveness.
With such embodiments, it is necessary to have the pre-grating cleaned manually on a preventive or regular basis or when the amount of clogging reaches a certain maximum level. Arrangements are sometimes made such as appropriate orientation of the pre-grating to facilitate the removal of the floating debris, or a descending shield to facilitate the sliding of the debris on the surface of the pre-grating, or a pre-grating set further forward to facilitate removal of the debris from above.
However, these arrangements are not always possible or easy to implement. Moreover, the automated cleaning systems required are expensive, bulky, and poorly suited for integration in a discreet or aesthetic manner.
Document FR-A-2835548 discloses a linear hinged module for unclogging the grating, comprising a scraper supported at the end of a movable arm, which makes this device unsuitable as has been previously indicated.
Thus, for a hydro-electric power plant comprising, operatively associated, a downstream turbine unit and an upstream grating assembly for allowing the inflow of water, there is a need to remove the floating debris stopped by the grating of the grating assembly to prevent the debris from passing through the impeller, in an effective, easy manner that is as inexpensive as possible, by means of an arrangement that is as simple, robust, and compact as possible.
The invention provides a solution to this problem.
U.S. Pat. No. 1,586,754 relates to a double rack for a water supply, with a pre-grating or front rack for stopping debris. The retaining grating or bottom rack is then inactive. When the double rack arrangement is in the upper position, the pre-grating or front rack is substantially horizontal and a valve is open, so that the debris that was on the pre-grating are sent into a tank and a passage connecting to a space. The water then passes through the retaining grating or bottom rack which retains the debris. After the pre-grating has been lifted, the door is opened and the water passes over the pre-grating into the channel or passage and, simultaneously, washes the debris from the pre-grating so it passes into the channel or passage around the turbine and travels downstream. Then the door is open or closed as desired.
As one can see, an embodiment according to U.S. Pat. No. 1,586,754 relates to a very specific hydro-electric power plant in which the turbine unit is of a very specific type and is in a very specific arrangement which have nothing to do with the type and arrangement of a turbine unit as described in document FR-A-2862723, the latter type and arrangement being the object of the invention.